I have trawled the internet seeking advice but to no avail. Any help would be greatly appreciated.

My project involves a background image. I have a circle acting as a mask, the circle is motion tweened to move around the image.

Now instead of completely hiding the rest of the image beneath the mask layer, is there any way that the image outside of the circle can be blurred? My aim is to use the motion tweened circle as a focus point on the image if you like.